A receptor for interleukin 10 is related to interferon receptors (1)
Interleukin 10 (IL-10) is a cytokine produced by activated T cells, B cells, keratinocytes, and monocytes/macrophages. Mouse and human IL-10 (mIL-10, hIL-10) inhibit cytokine synthesis by activated T cells, natural killer cells, and monocytes/macrophages and block the ability of macrophages to act as antigen-presenting or costimulatory cells.
Cells and cell lines representative of mIL-10-responsive cells were tested for ability to bind FLAG-mIL-10. A mast cell line(MC/9) and a macrophage cell line (J774) were found to give reproducible but low levels of specific FLAG-mIL-10 binding that were reduced to background by excess mIL-10 as a competitor. Sublines MC/9-b2 (three cycles) and J774-al (two cycles) expressing a significantly higher number of receptors were obtained. Two -3.6-kb cDNA clones, pM3.14 and pJ18, were isolated from the MC/9-b2 and J774-al libraries, respectively. COS7 cells transfected with the mIL-10R cDNAs specifically bound FLAG-mIL-10.
pMR29 encoded an open reading frame of 576 amino acids, including a putative signal peptide sequence of 16 amino acids, a 222-amino acid extracellular domain, a transmembrane segment of 24 amino acids, and a cytoplasmic domain of 314 amino acids. Structurally, the extracellular portion of mIL-10R consists of two homologous segments of -110 amino acids similar in size to the immunoglobulin-like ligand binding domains of the growth hormone receptor. The first class II CR domain has two conserved tryptophans and the second cysteine pair of class I CRs, whereas a unique disulfide loop is formed in the second domain.
mIL-10R+ cell line BaMR29a was tested for ability to bind 125I-hIL-10 and respond to mIL-10. BaMR29a cells expressed about 4000 mIL-10Rs and bound 125I-hIL-10 with a Kd of about 70 pM, a relatively high affinity among CRs. Neither BaF-Neo nor parental Ba/F3 cells gave a proliferative response to mIL-10, but BaMR29a proliferative response to mIL-10, but BaMR29a cells responded to mIL-10 in a dose-dependent fashion in an MTT assay.
Like the cellular cytokine, vIL-10 inhibits macrophage activation and stimulates human and mouse B cells, suggesting the possible existence of additional IL-10R components on B cells and activated macrophages.